Infectious sacroiliitis: value of computed tomography (CT) and magnetic resonance imaging (MRI)

Infectious sacroiliitis is an uncommon septic arthritis, the diagnosis of which is difficult to establish. We retrospectively examined 14 cases of septic sacroiliitis, by CT (two of whom also had an MRI examination). The patient population consisted of eight men and six women; 9 were African, 8 had tuberculous sacroiliitis and 6 pyogenic sacroiliitis. All the cases showed a pre-sacroiliac soft tissue swellilng with ring-like enhancement following intravenous contrast in eight cases. A gas image was observed at the centre of the abcess in two cases. Joint narrowing was found in four patients and widening in eight, associated with an image of bone sequestration in seven, CT gave an etiologic orientation in 8 cases, and facilitated the guidance of bone biopsy. MRI showed low signal T1-weighted images and high signal T2 of the subchondral bone, joint space and soft tissue abcess. We conclude that CT is helpful in the evaluation of infectious sacroiliitis, and that further studies are necessary to evaluate the role of MRI in such pathologic processes.